The present invention relates to a facsimile apparatus, and in particular to a facsimile apparatus which binary image processes the halftone read image data into different two or more gradients and is capable selecting and transmitting the image data having an appropriate gradient among binary image data which have been processed depending upon communication requirements including processing requirements at a receiving facsimile apparatus in consideration of the transmission period of time.
The facsimile apparatuses generally read the image of an original document by means of a reader and transmits the obtained image data to the other facsimile apparatuses over a transmission line.
Since the image data which is transmitted by the facsimile apparatus is binary data (1, 0) representing an monochrome image, it is necessary to process the read image into binary image data when the document has halftones. Various techniques for representing images by binary data including dithering technique and error diffusion technique have been proposed.
Although the dithering technique can shorten the period of time which is taken to transmit the image data, it provides a low image quality. Although the error diffusion technique can provide a high image quality, the period of time to transmit the image is extended. These techniques have advantages and disadvantages. A technique to address these problems is disclosed in Japanese Laid-open patent publication No. 8-204962.
This publication No. 8-204962 teaches that a scheme for processing halftone images so that they are represented by binary data is selected depending upon the recording line density of the facsimile apparatus which receives binary data.
FIG. 1 shows the flow of operation in the prior art apparatus. The operation of this apparatus will be described with reference to the drawing.
Facsimile transmission is generally conducted by receiving and detecting a digital identification signal (DIS signal) including information of the receiving capability at the receiving terminal and then transmitting a digital command signal (CDS signal) and a training signal for the purpose of phase matching of the signal rates of the image data, prior to the transmission of the binary image data to the receiving facsimile apparatus. If it is judged that the signal rate is such that the reception of the image data is possible, a facsimile apparatus at the receiving terminal which received the training signal responds the training signal with a responding signal (CFR signal) for confirming the ready state of the reception. If it is otherwise judged, the receiving facsimile apparatus responds the training signal with a training failure responding signal (FTT signal). If the transmitting (sending) facsimile apparatus receives the FTT signal, the data signal rate is lowered to a next lower rate at which the receiving facsimile apparatus can accept the data signal and the signal rate of the image data is determined by retransmitting the training signal for phase matching.
Also in the prior art, after passing the above-mentioned general procedure, it is judged whether or not the transmission mode specifies the halftone image. If the halftone image is specified, a scheme is selected to process the image so that the halftone image is represented by binary data for shortening the communication period of time.
In this art, if the recording line density of the receiving facsimile apparatus, which is detected from the DIS signal is 400 dpi, the read image data is binary processed by the error diffusion technique having a resolution of 400 dpi and is transmitted. If the recording line density is other than 400 dpi, the read image data is binary processed by the dithering technique having a resolution of 200 dpi and is transmitted. The prior art adopts a basic concept for selecting among halftone binary image processing techniques such as error diffusion and dithering techniques.
However, the technique which is disclosed in the above-mentioned Japanese Laid-open patent publication No. 8-204962 has a problem as follows: If the above-mentioned scheme for binary processing the halftone image is selected, the signal rate may often be lowered due to phase matching between the transmitting and receiving facsimile apparatuses while the recording line density of the receiving apparatus can be recognized from the normally received DIS signal, in case of overseas communications in which the signal level is generally deteriorated or in which the quality of the transmission line is not excellent.
Since the scheme of binary processing of the halftone image is selected based upon the information of the receiving capability (recording line density) of the receiving facsimile apparatus by the technique of the Japanese Laid-open patent publication No. 8-204962 in such a case, if the binary image processing for higher image quality is selected by detecting the DIS signal which is transmitted from the receiving facsimile apparatus, the data transmission rate may be lowered due to the phase matching, resulting in an extension of the transmission period of time.
It is an object of the present invention to provide a facsimile apparatus for transmitting image data, which is capable of keeping the image quality of the received image in a range which is proper to the transmission rate without extending the transmission period of time in consideration of the data transmission rate which is varied depending upon the communication conditions including the conditions of the transmission line between the transmitting and receiving facsimile apparatuses and the processing conditions at the receiving facsimile apparatus.
It is another object of the present invention to provide a facsimile apparatus which is capable of shortening the transmission time without extending thereof even if the data signal rate is lowered by optically reading the image of a document to convert the image data which is output as halftone image data into binary halftone image data in which binary pixels are differently arranged depending upon the gradient of the document, and by selecting an appropriate gradient among the resultant binary data representing two or more different halftone images depending upon the transmission rate of the signal which is determined by the phase matching of the data signal rate between the transmitting and receiving facsimile apparatuses.
The facsimile apparatus of the present invention comprises an image reading unit for reading the image of an original document, a binary processing unit for generating binary image data having different two or more gradients representing halftone images, a modem and line control unit for conducting communications between transmitting and receiving facsimile apparatuses over a communication line, and a central processing unit for outputting the binary image data as transmission data to the modem by selecting the gradient depending upon the signal rate which is determined by the phase matching the transmission data rates between the transmitting and receiving apparatuses. When the image of the halftone document is transmitted, the facsimile apparatus of the present invention conducts the phase matching of the data signal rates of the image data between this transmitting and the receiving facsimile apparatuses by the central processing unit via the transmission line, the line control unit and the modem and the central processing unit selects binary data representing halftone image which is generated by the halftone image binary processing method having an appropriate gradient based upon the data signal rate of the image data which is determined by the phase matching. The binary data of the halftone image is provided by reading the document as the image having a halftone density by means of the reading unit and by converting the read image data into binary data in accordance with a halftone image binary processing method by means of the halftone image binary data processing unit. The binary data which is output from the halftone image binary data processing unit is transmitted to the receiving facsimile via the modem, line control unit and transmission line.
It is a further object of the present invention to provide a facsimile apparatus, in that the apparatus comprises a central processing unit for controlling the whole of the facsimile apparatus, an image reading unit which is capable of optically reading an image of an original document to be transmitted to output the read image as data representing halftone images, a halftone image binary processing unit for converting the image data representing halftone images, which is output from the reading unit into binary image data, having different two or more gradients, in which the binary pixels are differently arranged depending upon a gradient, a modem for conducting modulation and demodulation between binary image data including the image data from the halftone image binary processing unit and a transmission signal which is transmitting over a communication line, and a line control unit for controlling the communication line on which transmitting facsimile apparatus communicates to receiving facsimile apparatus, wherein the gradient is selected from the binary image data which is generated by the halftone image binary processing unit depending upon the data transmission rate which is determined by phase matching between the transmitting facsimile apparatus which transmits the binary image data and the receiving facsimile apparatus which receives the transmitted binary image data and wherein the obtained data is used as a transmission signal.
It is a further object of the present invention to provide a facsimile apparatus in that higher and lower image quality data is selected among the binary image data having different two or more gradients, which is generated by the halftone image binary processing unit if the data transmission rate which is determined by phase matching between the transmitting and receiving facsimile apparatuses is higher and lower, respectively.
It is a further object of the present invention to provide a facsimile apparatus in which the binary image data which is generated by said binary processing unit for the halftone image is reselected in accordance with the image quality of the receiving facsimile apparatus if the receiving facsimile apparatus which receives the binary image data has a lower image quality than that is selected depending upon said data transmission rate.